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AR# 2881

Description

General Description:You may receive the following error when using the JTAG Programmer:

JTAG Programmer Started 1997/09/29 10:03:29

Loading Boundary-Scan Description Language (BSDL) file 'C:/Xilinx/data/xc9536.bsd'.....completed successfully. Checking boundary-scanchain integrity...ERROR:basut - Boundary-scan chain test failed at bit position'0' on instance 'At17cisp(Device1)'. Check that the cable, system and deviceJTAG TAP connections are correct, that the target system power supply is set tothe correct level, that the system grounds are connected and that the parts areproperly decoupled.

Solution

Chain integrity must be assured before the results of the Boundary Scan testing can be relied upon. A chain may have many faults that can interfere with the integrity of the chain, e.g.

A component in the chain may be missing, dead or incorrectly loaded.

A component in the chain may have a broken connection on one of its TAP pins.

A TDO to TDI connection between two components could be shorted to another node.

A component in the chain may not have sufficient power supply.

System or Clock noise could cause a component in the chain to jumpTAP states.

A combination of all the problems described above may exist in a chain of components making it very difficult to diagnose.

The JTAG Programmer performs the integrity test by relying on the ICs ability to write a fixed data pattern in its Instruction Register in the Capture-IR state of the TAP Controller. This concatenated data can then be shifted out on the TDO pin of last IC. The value of attribute INSTRUCTION_CAPTURE in the BSDL (Boundary Scan Description Language) file for each device in the chain shows what this data will be. Additionally, the IEEE standard 1149.1 mandates that the two LSBs of this data should be "01".

For a simple test case, assume that there are three devices in the chain and the Instruction Registers are only two bit wide. In this case, for a good chain we will see a data of "010101" coming out on the TDO pin of the last IC.

As an example of a bad chain assume that there is something wrong with the connection of the first device in the chain. This device then will not output a "01" on its TDO pin. Instead, it may push a value such as "11". We will see a data of "110101" coming out on the TDO pin of the last device. By examining the data stream closely, we can see that the last two devices in the chain are connected properly and there is a problem with the first device in the chain.

The JTAG programmer will issue a 'Boundary Scan Integrity' error if receives unexpected data at the TDO pin of the last IC. The integrity failure can occur for a single device as well as for multiple devices in the chain.